When workpieces are machined with a machine tool, several types of tools may be used for machining one workpiece. When the several types of tools are used for machining, a machine tool provided with a tool exchange device configured to exchange tools is used. The tool exchange device can exchange tools automatically, for example, according to a machining program.
The tools may be broken while machining workpieces. It is known that the machine tool is provided with a tool shape measurement device in order to confirm soundness of tools. The tool shape measurement device can determine whether or not tools are damaged by measuring shapes of the tools. The shape of the tool includes, for example, a tool length and a tool diameter. Items for inspection of the tool shape include partial damages or breakages of surfaces of the tools.
The contact type device that measures shapes of tools by bringing a probe or the like into contact with the surfaces of the tools is known as an example of tool shape measurement devices. The image pickup type device that captures an image of the shape of the tool with a camera and calculates the shape of the tool by analyzing the captured image is known as an example of tool shape measurement devices.
Japanese Unexamined Patent Publication No. 6-134638A discloses a pattern collation and recognition apparatus for tools that includes a photographing device such as a CCD camera disposed so as to face a measurement position in a magazine and an illumination device disposed so as to oppose the photographing device. In addition, it is disclosed that illumination device illuminates the tool from behind by using a diffuser panel. Furthermore, it is disclosed that the photographing device captures a tool pattern image formed by backlight of the tools.